In the welding of lengths of pipe to one another to form a large diameter pipeline it is conventional to make use of an internal clamp mechanism and to position it adjacent the free end of a first pipe with a portion of the clamp extending beyond the free end of the pipe so as to be accommodated within a second pipe that is to be welded to the first pipe in axial alignment therewith. The internal clamp mechanism conventionally has two sets of axially spaced, circumferentially arranged clamp members which may be expanded into forcible engagement with the inner surfaces of the first and second pipes adjacent their confronting ends so as to reform the confronting ends of the two pipes into matching configurations, following which the pipes are welded to one another. After completion of the welding operation, the clamp members are contracted, thereby enabling the clamp mechanism to be moved longitudinally of the second pipe toward the free end thereof in readiness to join thereto a third pipe.
In those instances in which an internal clamp is precisely aligned with the longitudinal axes of two pipes and wherein the confronting ends of the two pipes are of uniform diameter and of uniform wall thickness, satisfactory welds can be made. It is extremely rare, however, that the wall thicknesses of two confronting pipes are uniform, especially in pipes having diameters of five feet, more or less, and it is more common than not for the longitudinal axis of the clamp to be somewhat misaligned with the longitudinal axis of one or both of the pipes that are to be joined together. As a result, it is rare indeed, in field operations, for one length of pipe to have its longitudinal axis in perfect alignment with the longitudinal axis of the pipe to which it is joined. More often than not, the axis of one pipe will be offset laterally to one side of the longitudinal axis of the adjacent pipe, as a consequence of which a step exists at the joint between the two pipes. Thus, on the inside of the pipe joint there is a non-uniform condition known as high-low, or simply hi-lo, which is most undesirable and often results in the necessity of having to reweld the joint at substantial expense. To avoid the need for rewelding as much as possible, an inordinate amount of time currently is consumed in attempting to match the confronting ends of two pipes that are to be welded together, thereby adding considerably to the cost of forming pipelines.